This invention relates to a process for the optimized heat transfer from carriers of reversible, heterogeneous evaporation phenomena for the purpose of heat generation or refrigeration, this process utilizing the principle of the heat pipe. Heat pipes are known from U.S. Pat. No. 2,350,348 and from the puplication by P. D. Dunn and D. A. Reay, Heat Pipes, Pergamon Press, 1976. Due to their outstanding heat transport performance, they are accepted in industry to an increasing extent. Particularly simple to manufacture are heat pipes which operate according to the thermosiphon principle. However, it is a requirement hereof that the evaporation zone of the heat pipe is arranged beneath the condensation zone.
Reversible, heterogeneous evaporation is a generally known principle and may proceed with or without chemical change. For example, the gas absorption on carriers such as activated charcoal is of a purely physical nature. Examples of reversible, heterogeneous evaporation phenomena with chemical conversion are the formation and decomposition of metal hydrides and ammoniated salts like calcium chloride ammoniacate. Independently of whether these processes are of a chemical or physical nature, the evaporation or ejection process is always endothermal while the oppositely directed absorption process proceeds exothermally.
The use of reversible, heterogeneous evaporation processes on a carrier always suffered in the past from the substantial disadvantage that the heat transfer from the carrier to its environment proceeds only very slowly and with very low efficiency because the carrier materials generally exhibit poor heat conductivity. This results in undesirably long cycle times when operating periodically operated apparatus such as refrigerating machines or heat pumps as well as in correspondingly largely and voluminously designed apparatus because the heat transport performances or efficiencies required can only then be achieved.
In U.S. Patent application Ser. No. 268,970, filed June 1, 1981, a process and an apparatus for the energy-saving recovery of useful or available heat from the environment or from waste heat have been proposed. In this process, there is utilized, for example, the heat reaction taking place as a metal hydride is formed and decomposed. In a preferred embodiment, the reversible heat exchangers are replaced by heat pipes. In the apparatus described in this patent application, the upper or lower end of a heat pipe extends into the reservoir containing the metal hydride and carriers off the heat or cold generated by the reaction via the heat pipe. Heat transfer from the metal hydride as the carrier to the heat pipe takes place only in a relatively small region and, consequently, is only very slow and incomplete.